In the Digital Video Broadcasting over Terrestrial 2 (DVB-T2) system, since various spectrum reverse operations may be involved during signal processing, a signal received from an antenna may be a correct spectrum or a reversed spectrum, and the reversed spectrum is equivalent to swapping cosine and sine components in the correct spectrum in the time-domain. To prevent errors from occurring during subsequent data demodulation due to the signal with a reversed spectrum, the receiver first determines whether the received signal is a correct or reversed spectrum and then switches connections of a multiplexer accordingly to transmit the correct signals to subsequent processing circuits—such approach however needs a rather longer detection time to undesirably affect processing performance of the receiver.
Further, orthogonal frequency-division multiplexing (OFDM) is implemented in the DVB-T2 system, and thus significant inter-carrier interference (ICI) is present in the receiver. To lower the ICI, the receiver generally adopts a circuit for improving carrier frequency offset. Therefore, it is an important task to provide a circuit with a minimal cost and a method with optimal efficiency for improving the carrier frequency offset.